The present invention relates generally to dental implants, and more specifically to a dental implant having an improved asymmetrical configuration to take advantage of the bony topography that is often present immediately following tooth extraction prior to any healing or remodeling process. The asymmetrical dental implant is primarily intended, but not limited to, placement in the upper anterior region of the mouth immediately following tooth extraction.
Dental implants are used in place of missing natural teeth to provide a base of support for single, multiple teeth or full arch prosthetics. These implants generally include two components, the implant itself and the prosthetic mounting component referred to as an abutment upon which the final prosthesis is installed. The implant has apical and coronal ends, whereby the coronal end accepts the base of the prosthetic abutment using connection mechanisms of different designs. One such mechanism is a deep female conical receptor with an internal alignment or anti-rotational element such as a hex, double hex, spline or other single/multi sided arrangement used for prosthetic alignment and anti-rotational stability. Deep female conical connections have been shown to be the most stable at preventing micro movement between the implant body and the abutment under normal loading conditions. It has been suggested that preventing micro movement is one of the key factors required for crestal bone maintenance.
Dental implants are also used in place of extracted (and/or missing) natural teeth not only as the base of support for an abutment and final prosthesis to restore normal oral function, but also to prevent bone loss that normally occurs following tooth loss. Once a tooth has been extracted, the bone from which the tooth originated heals and is forever changed. Accordingly, while dental implants should be designed to take into account this natural healing process of bone after tooth loss, this is seldom the case.
Attempts by others like Elain (U.S. Pat. No. 6,854,972), Mundwiler (U.S. Pat. No. 7,329,124) and Wohrle (D,511,833 and U.S. Pat. No. 6,283,754) have focused on single stage implant designs with a soft tissue collar extending above the bone interface level. This presents several problems. Immediate placement single stage implants do not lend themselves to grafting procedures as the implant cannot be buried (two staged) and covered with a membrane to allow the gap between the implant and the extraction wall socket to fill with new bone. When implants are placed immediately they are essentially placed into an open wound. Covering this open wound with a membrane such as the PRF (platelet rich fibrin) membrane is extremely important since getting primary wound closure is difficult. PRF membranes due to their biocompatibility and slow release of human growth factors not only stimulate bone fill under the membrane, but also encourage soft tissue overgrowth and wound closure as well. Further, with the asymmetrical design, any collar above the bone interface would be pointed in the wrong direction since the implant is placed at an axial inclination following the root direction of the tooth being extracted and replaced by the implant. Axial redirection of the implant abutment ideally would originate from bone level with a custom zirconia abutment utilized to prevent graying of the overlaying soft tissue. This is extremely important in the upper anterior region of the mouth and another reason a single stage implant with single stage collar that transverses the overlaying soft tissue is contraindicated. Furthermore, attempts mimicking the cemento-enamel junction (CEJ) of the natural tooth do not take into account the healing morphology of the bony anatomy particularly when the implant was placed following the immediate placement protocol.
In practice, the implant body is surgically inserted in the patients jaw and becomes integrated with the bone. This can be done immediately at the time of tooth extraction or more typically in a delayed manner allowing healing and remodeling to occur first. More specifically, the implant body is screwed or pressed into holes drilled in the respective bone or the apical end of the extraction socket is prepared to accept the insertion of a dental implant immediately. The surface of the implant body is characterized by macroscopic and microscopic features that aid in the process of osseointegration. Once the implant is fully integrated with the jaw bone, or in some cases at the time of insertion, the abutment is ready to be mounted. For two-stage implant designs, the abutment passes through the soft tissue that covers the coronal end of the implant after healing and acts as the mounting feature for the prosthetic device to be used to restore oral function. Implants of the single-stage design extend at least partially through the soft tissue at the time of surgical insertion. The coronal end of the implant body acts as a built-in abutment with the margin of the coronal collar usually being employed as the margin of attachment for the prosthesis used to restore oral function. These components, the implant and abutment, are typically fabricated from titanium or titanium alloy as well as zirconia based, alumina based or sapphire based ceramics. In some instances, ceramics and metals are combined to make a single component, though this is usually limited to the abutment component of the implant system. There is promising research on the use of titanium zirconium alloys as well.
Implant designs have gone through a considerable amount of trial and error in an attempt to deal with the issue of the bone not healing evenly once a tooth has been extracted. It has been found that bone heals based on the principles of bone biology, surrounding bone anatomy, surrounding bony and soft tissue anatomy as well as blood supply to the area. To a certain degree, bone healing and/or remodeling is also influenced by the placement and subsequent loading of an implant fixture in the area of the extracted tooth. Only a limited number of studies have been conducted regarding bone loss patterns following tooth loss. One such study, by Cawood and Howell was published in the International Journal of Oral and Maxillofacial Surgery in 1991.
One can construe from this (and other) studies that for a time period as short as several months, the highest point of bone anatomy is at the lingual side of the extracted teeth after healing. Due to the natural bony contours in the anterior area of the upper jaw, this healing pattern, often referred to as facial collapse of bone, is more immediate than in the posterior upper and lower jaw.
If an implant fixture is placed in the center of the maximum height of available bone, the implant can end up too far to the lingual from the point of view of the restorative dentist. To avoid this overly lingual placement, surgeons have utilized numerous ways to position implants. One such way is to submerge the implant even to the facial level of bone such that the implant placement compensates for the contour of the healing bony topography. Accordingly, as the implant must be shorter in length than ideal, together with the increase in crown to root ratio, a weaker and less stable implant/abutment complex results.
Another problem with burying implants is that loading forces typically produce a bone loss pattern referred to as cupping. In the 1980's one of the most commonly placed implant designs was the Branemark type dental implant. These implants are ideally positioned in the approximate center line of the space where the extracted tooth was previously located. As with most traditionally designed implants and (even most today), the Branemark type fixture relied on a flat to flat matting surface perpendicular to the long axis of the implant body as the mating interface when joining the implant and the abutment together. This design usually displays a bone loss pattern described as a cupping of the bone at the coronal end of the implant once loaded with occlusal forces. This cupping pattern usually stabilizes after about one year of function with vertical bone loss of approximately 2 mm but, by that time, loss of bone critical to the predictable support of overlying soft tissue is lost.
Another way to avoid overly lingual placement is to install the implant so that it is protruding relative to the sloping bony anatomy. While maximum height of available bone may be engaged, the exposed threads of the implant compromise the ideal facial contour of the final restoration.
In an attempt to avoid these problems, surgeons may opt to purposefully misalign the implant by angling it towards the lingual (for example). In other words, the implant is placed in the middle of the highest point of bone lingual to where the missing tooth was previously positioned. However, this kind of implant positioning may actually create the greatest problem for the restorative dentist as he must now attempt to position the abutment and final restoration in an off axial alignment with respect to the implant. Proper alignment of the dental implant is essential to the esthetics as well as the mechanics of proper oral function. If the abutment and crown are misaligned to the implant, the tooth not only looks unattractive, but it may not be able to function properly due to unfavorable loading forces.
There are dental implants systems that typically do not demonstrate a cupping bone loss pattern or some of the other previously mentioned problems. The two most common of such are the Astra Tech and Ankylos systems. Both of these implant designs have an internal female conical connection and do not rely on flat to flat mating surfaces at the implant/abutment interface which would typically be perpendicular to the implant fixture's long axis. However, the Ankylos surgical protocol demands placing the implant two millimeters below the crest of bone in the upper anterior region of the mouth which essentially creates a cupping or defect of the crestal bone.
The Astra Tech system, on the other hand, has been shown to maintain crestal bone when placed at bone level. Astra Tech offers implants with a sloping contour of the coronal or top of the implant fixture such that the lingual bone is engaged and preserved. This coronal contour can be a straight line or a slightly convex contoured design so long as one bone engaging side of the implant body (which would become the lingually oriented side of the implant fixture) is longer in the apical-coronal bone engaging dimension than any other apical-coronal bone engaging dimension. In particular, U.S. Pat. No. 7,270,542, to Cottrell, incorporated herein by reference, is directed to such a modified sloped top dental implant fixture. Dental implants made to these design specifications make it easier for surgeons to place implants ideally and maintain the bony topography after healing remodeling has occurred.
The Astra Tech system mentioned above has essentially been modified to develop the sloped top fixture which now has been granted FDA approval. Much of this success is credited with Astra Tech implants having a combination of a rigid conical abutment connection and the presence of coronal stress reducing micro threads on the implant body which greatly reduce and in most cases eliminate the aforementioned bone loss patterns.
Astra Tech has addressed coronal bone loss by introducing micro threads at the coronal portion of the implant body to distribute forces transferred to the surrounding bone combined with a female conical connection that eliminates micro movement in addition to dissipating lateral loading forces. Sloping the top of the fixture to follow the healing bony topography for delayed dental implant placement has been shown to be very effective during clinical trials. Other attempts to enhance implant designs have focused on the coronal aspect of the implant body in hopes that mimicking the natural CEJ anatomy or shaping the implant body to be more root like in character would be effective. Implants duplicating tooth anatomy in some way, shape or form have not had the same level of clinical success as the sloped top design.
However, while the sloped top implant works very well with extraction sites that have been allowed to heal, and the implant placed following the delayed protocol, it may not be the most ideal design when implanted immediately following tooth extraction. It is believed that a refinement of the sloped top implant design could possibly enhance the maintenance of the presenting bony architecture following tooth extraction utilizing immediate implant placement protocol. While this would involve an attempt to defy Mother Nature and the typical bone healing and remodeling process following tooth extraction when done in conjunction with promising new bone grafting techniques, most specifically utilizing platelet-rich fibrin membranes, which provides a much slower release of human growth factors, such bone maintenance has promising potential. But fooling Mother Nature does have certain limitations. Implants placed immediately do not fill the entire extraction socket as implants are generally somewhat undersized compared to the natural tooth they are replacing since it has been shown that implants cannot be as close to neighboring natural teeth as the natural tooth being replaced. Consequently there is a gap between the coronal aspect of the extraction socket and the immediately placed dental implant. This gap is greatest on the facial aspect as immediate placement protocol positions the fixture against the lingual wall of the extraction socket taking into account the previously mentioned facial collapse of bone. Also, at the coronal aspect on the mesial and distal sides on the implant there is a gap as well with only the apical end of the implant firmly anchored in bone. Accordingly, some remodeling is going to take place as these gaps fill in with new bone even when new bone is harvested while preparing the apical aspect of the extraction socket to accept the dental implant and used to fill the coronal aspect of these openings or gaps. The objective is to design a coronal contour of the dental implant that anticipates how this will occur when immediate implant placement protocol is undertaken. Thus a compromise must be established between the bony contours that exist around the coronal contour of the extraction socket and the contours of the asymmetrical dental implant which best takes into account the angulation that the implant must follow in the extraction socket while anticipating the remodeling process compared to the delayed implant placement protocol with the typical sloping crestal ridge topography.
Accordingly, it is a general object of the present invention to provide for improved alignment at the top of implant fixture with the surrounding bony anatomy available at the time of extraction so when the implant is placed following the immediate placement protocol, the contours anticipate the amount of bony remodeling that will take place and then maintain and preserve this bony architecture.
It is a further object of the present invention to overcome the unsolved challenge of maintaining at least some of the interproximal bone height that has to date been impossible to maintain.
It is another object of the present invention to provide a modified dental implant design combining the elements that are known to work in overcoming crestal bone loss such that the problems related to immediate implant placement with respect to maintaining the natural bony topography present at the time of tooth extraction can at least be partially accomplished.
It is yet another object of the present invention to enable implants to be placed in immediate surgical extraction sites preventing or reducing the amount of natural healing remodeling typified by the bony anatomy following tooth extraction and subsequent remodeling which is typically higher on the lingual aspect healed extraction site and maintain more interproximal bone height which has not been successfully accomplished to date.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.